Embodiments of the invention generally relate to imaging, and more particularly to reconstruction of computed tomography data.
In a typical computed tomography (CT) system, an X-ray source projects a fan-shaped or cone-shaped beam, which is collimated to lie within an X-Y plane of a Cartesian coordinate system termed the “imaging plane.” The X-ray beam passes through an object being imaged, such as a medical patient, and is incident upon an array of radiation detectors. The detector array includes detector elements, each of which measures the intensity of transmitted radiation along a beam projected from the X-ray source to the particular detector element. The intensity of the transmitted radiation is dependent upon the attenuation of the X-ray beam by the object and each detector produces a separate electrical signal that is a measurement of the beam attenuation. The signals are processed and reconstructed to form images which may be evaluated themselves or which may be associated to form a volume rendering or other representation of the imaged region. In a medical context, pathologies or other structures of interest may then be located or identified from the reconstructed or rendered volume.
During the past few years, the use of cone-beam tomography has become more prevalent. Various techniques that allow accurate reconstruction for many different source trajectories (such as helix, saddles, variable pitch helix, circle-plus-arc, and so forth) have been developed. Progress has also been made on developing algorithms for trajectories that do not satisfy Tuy's completeness condition everywhere in the imaging volume such as for the circular trajectory and for the circular segment trajectory. These trajectories satisfy Tuy's condition only at certain points within a single plane, yet data acquired along these paths may be used to reconstruct volumetric data, resulting in reconstructed images that may exhibit cone-beam artifacts.
Cone-beam artifacts degrade the quality of the reconstructed CT images. Moreover, as CT scanners evolve to larger coverage, such artifacts may become more problematic. For example, cone-beam artifacts produce shading and glaring around high contrast edges in CT images. These artifacts are undesirable and may sometimes affect the quantitative robustness of CT numbers. Moreover, conventional techniques fail to provide desired imaging quality due to cone-beam artifacts. Also, use of other currently available techniques result in new artifacts being introduced due to data truncation, additional interpolation and filtering. Further, traditional techniques of cone-beam reconstruction use weighting of different parts of the data by different amounts that result in high computational cost and time.
It is therefore desirable to provide an efficient and computationally less intensive reconstruction technique and to reduce cone-beam artifacts in CT images without compromising on image quality.